Trailers have long been used to transport boats over the road. In most cases, for most boats which are small enough to be moved and launched by the user, the trailer consists of a frame with a cradle to hold the boat, with a raised portion in front to attach to a ring in the bow of the boat. The cradle may be formed of rollers or of padding-covered flat props.
When the boat has been driven to the body of water in which it is to be used, the trailer is backed down a ramp, and the boat is released into the water. For retrieval, the process is reversed.
In most cases, the retrieval process involves submerging the trailer to a greater or lesser degree. The boat is then floated up over the trailer, the bow fastened to the front of the trailer, and the trailer is pulled out of the water. As the trailer is pulled up the ramp, the boat settles onto the trailer, ready for transportation over the road.
If the cradle on the trailer is of the kind provided with rollers, the trailer need not be fully submerged, as the boat can be pulled up the rollers by means of a winch or the like. Schroeder, U.S. Pat. No. 2,586,485, Carbone, U.S. Pat. No. 4,620,716, and Ullman, U.S. Pat. No. 3,974,924, show three of the many patents on roller-keel trailers in which the varying number and arrangement of rollers on the keel are expected to exert a centering action, once the boat has settled onto them. These rollers can do little or nothing when the boat is floating in the water above them, as is the case when the trailer has been backed into the water. If the trailer is not submerged, then the rollers can act to a greater or lesser degree to center the boat, but at the cost of having to actually winch the boat out of the water with the guide rope, which takes far more effort than merely centering the boat and driving the trailer up the ramp.
Trailers without rollers must be submerged entirely, and then driven out of the water with the boat on them, as the boat will not easily shift once it is resting on the padded props.
While this process sounds simple in theory, in practice the actions of wind, waves and water currents make retrieving a boat much more complicated. The boat can be easily attached to the winch at the bow, but if it is not accurately aligned on the trailer it will not settle properly into its cradle as it is pulled out of the water.
The wind can exert a major force on a small boat--in fact, it is more of a factor in small, light boats which are easily blown about than in larger, heavier boats. The boat will tend to weathercock in the wind, pivoting around the bow attachment. It does not take much wind to blow the boat fully sideways, right off the trailer, before the owner can get into the car and pull it out of the water.
In rollerless trailers, there is no centering tendency at all--however the boat settles, there it will ride. In a worst case, the boat could be damaged as it lands incorrectly and bounces on the props under wave action.
Tilting trailers, where the tongue breaks and allows the trailer to articulate, can alleviate the problem to a minor degree. However, this requires extensive modification to the design of the trailer, can weaken the structure, and cannot easily be added to existing trailers in the field.
There have been a number of attempts in the past to devise trailers which will center the boat, but they have not met with commercial or practical success. The following patents are offered as examples of the different types of boat-guiding trailers, and are not intended to be an exhaustive list of all such trailer patents.
Tingley, U.S. Pat. No. 4,684,145, shows a pivoting bow guide which is mounted in the rear third of the trailer and pivots forward, sliding down the bow and under the keel, as the boat is pulled onto the trailer. Like all bow guides, Tingley's device is of little use in crosswinds, as the rear of the boat is free to weathercock as the bow is pulled forward. Further, his guide will work properly only with boats having smoothly tapered keels as shown in the patent--a flat-bowed boat, or one without a sharp keel (most fiberglass boats) will not center properly with this guide.
Kehne, U.S. Pat. No. 5,152,657, shows another pivoting bow lever. Kehne has the opposite intention of the present invention and Tingley, in that the lever is pulled upward with a cable to lift the bow and force the boat off the trailer.
Backus, U.S. Pat. No. 2,827,304, is an example of another class of boat-centering devices using upright posts at the rear of the trailer to guide the boat as it is pulled up onto the trailer. This kind of guide looks good in theory, but in practice in a crosswind the boat tends to push against the downwind post. which retracts against its spring, and the boat does not then center properly. Such a guide will prevent the boat from weathercocking completely perpendicular to the trailer, but it will not center accurately enough for the boat to ride correctly, especially on rollerless trailers. Backus' modification of the general design, using intermeshing gears to move both guides in tandem, would exaggerate the problem, as pressure against the downwind guide would open the pair excessively and the boat would be even less likely to center properly.
Another drawback of all boat guides which mount at the rear of the trailer, of whatever kind, is that it becomes necessary to enter the guides from the rear. In practice, this means that the boat usually has to be pushed backwards into the water and then guided back through the guides. This can be very difficult with larger boats or windy conditions.
A number of patents have been granted on trailers which include floating or levered boat cradles which completely surround the boat, parallel to the water surface. Fond, U.S. Pat. No. 5,165,706, and Ernst, U.S. Pat. No. 5,013,206, are examples of this kind of trailer. While this type of trailer does eliminate the weathercocking problem completely once the boat is in the cradle, it adds significantly to the weight, cost and complexity of the trailer, and cannot easily be added to an existing trailer.
Aasen, U.S. Pat. No. 4,209,279, shows a loading guide which, like the present invention, can be added to existing trailers, and which acts to guide the bottom of the boat as it settles onto the trailer. However, it has a number of drawbacks. Like the rear post guides, especially Backus, the boat would tend to push against the downwind guide and resist centering, and the linked guides would tend to exacerbate this effect. Also, like Tingley, the design is limited to boats with sharp, evenly tapering keels, on which the guides can evenly ride sideways as the boat settles. This design would be useless in a semi-catamaran design, where there are multiple parallel keels, as the guides would tend to hang up between the keels. On a flat bottomed boat with a thin keel, such as is commonly found in aluminum boats, Aasen would have no centering effect at all.